Pneumatic rubber tires include sidewalls, and in many cases are made with decorative sidewalls colored in contrast to the tread, such as white sidewalls colored with a titanium dioxide pigment. Sidewalls are continuously subjected to distortion under their normal operating conditions, and the sidewalls are subject to extensive flexing and can crack. In addition to such flex-cracking, such sidewalls are also subject to atmospheric chemical action such as by ozone attack, and the overall effect is that the sidewalls erode and degrade and can even separate from the tire carcass during use.
One prior composition which has been developed for overcoming these problems is disclosed in U.S. Pat. No. 3,508,595 to Wilson, and assigned to the General Tire & Rubber Company. This patent discloses a blend of chlorobutyl rubber, natural rubber, and ethylene propylene terpolymer as the protective cover for the white sidewalls used in such pneumatic tire construction. In column 4 of this patent it is also disclosed that other ingredients can be included in this triblend composition, and in a typical composition it is disclosed that 12 parts of naphthenic oil is included in an overall blend of 224.24 parts. The oil in this case, however, is a separate component added to the triblend composition which already includes the ethylene, propylene terpolymer.
U.S. Pat. No. 3,630,974 to Ladocsi et al, assigned to Esso Research and Engineering Company, further discloses the use of terpolymers for blending into high unsaturation rubbers in order to enhance their static ozone resistance. This patent also discloses a triblend of halobutyl rubber along with a terpolymer and a high unsaturation rubber in order to improve dynamic ozone resistance and heat flex resistance. The terpolymers employed by this patentee comprise ethylene, propylene and a diene, and the high unsaturation rubber can include natural rubber, styrene butadiene rubber, etc. It is again noted that various fillers can be used in connection with these compositions, and among the variety of materials listed are various "oils" along with resins, waxes, etc. The patentee specifically discloses the use of 10 parts oil per 100 parts of rubber in these final blends. This patent also discloses that the terpolymer used will not include more than 10 or 20% of the diolefin therein. It is also noted that while U.S. Pat. No. 3,865,763 to Feniak, assigned to Polysar Limited, is primarily concerned with stabilization of halogenated butyl rubber with boron compounds, example 5 of that patent discloses a combination of brominated butyl rubber with both an ethylene propylene rubber and an SBR rubber.
Finally, U.S. Pat. No. 3,830,274 to Waser, Jr., assigned to the Goodyear Tire and Rubber Company, discloses yet another elastomer blend for use in pneumatic tire sidewall compositions, in this case employing an ethylene propylene conjugated diene terpolymer along with bromobutyl rubber and a cis-1,4-polyisoprene rubber such as natural or synthetic natural rubber, along with a rubbery cis-1,4-polybutadiene with a particularly claimed molecular weight distribution. The patentee claims that this blend provides substantially improved hot flex-life and carcass adhesion properties for tire sidewalls.
Oil-extended terpolymers are also now known. These elastomers, such as VISTALON 3777 marketed by Exxon Chemical Co., are terpolymers of ethylene, propylene and a diene extended with about 75 phr of a paraffinic oil. These materials have been found useful in certain mechanical applications, such as hoses, and various extruded parts.